The Third Sister
by SiriusMarauderFan
Summary: In which Catherine Potter may not be who she's always thought she was. one shot, adopted Narcissa!AU


**Author's Note:** Thanks to my team for being so supportive as always! :)

Written for...

Quidditch League Fanfiction Competition. _Team/Position:_ Holyhead Harpies, Seeker. _Task:_ Write about a buried Truth being unearthed after decades and its consequences

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 **The Third Sister**

 _1,340_

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It wasn't like she had gone looking for answers to the inconsistencies she had noticed her whole life, like why there weren't any photographs of her before she was six months old, or why she didn't look anything like her parents.

No, the answers had come to her in the form of Bellatrix Black, pulling Catherine into a corner and pinning her there.

"Do you know who you are?" Bellatrix questioned.

Catherine had to read the older woman's lips to understand. She sighed to herself, pulling out a notepad and pencil. She wrote: 'Can I help you?'

Bellatrix's eyes scanned the paper for a moment and seemed to soften. She pulled away from Catherine, taking a step or two back but still blocking her way out of the Ministry corridor. "I need to know what you know."

'About what?' Catherine wrote. She had never spoken to Bellatrix when they were in school. There were four years and a house rivalry between them and she'd had no need to speak to her.

"About who your parents are."

Catherine pursed her lips, scribbling in her notepad furiously. She'd had quite enough of the teasing of her family and she was more than sick of it. She'd thought things would get better now that she was out of Hogwarts. She and Bellatrix were grown up now; surely they didn't need to take petty jabs at each other's family.

'Fleamont and Euphemia Potter.'

"You know that's not true."

Catherine shook her head, confused by the accusation. If not the Potters, then who? They were the ones who looked after her for eighteen years, who had taken her to St. Mungo's every few months for treatments that, in the end, had done nothing to cure the rare disorder that prevented her from hearing.

"You're adopted. I can prove it." Catherine watched intently as Bellatrix pulled out an old, faded photograph and handing it over. It was of two tiny dark-haired girls sitting on a bed, an infant laying across their legs. "This is the only photograph of my sisters and I," Bellatrix said, pointed to each of the children in turn. "Me, Andromeda, and Narcissa."

Catherine remembered Andromeda from school. She had been a Slytherin too, but not as antisocial as her older sister. She remembered the scandal of a Black being found in the Astronomy Tower with a Muggle-born boy. But there hadn't been another Black sister, to her knowledge.

Bellatrix noticed her confusion and continued. "Narcissa was born with a rare condition. She was deaf and there was nothing the Healers could do for her. My father decided that she wasn't worth keeping, that she wouldn't be able to learn or control magic, and that he needed to get rid of her."

Catherine felt her mouth go dry at the thought. The Healers her parents had taken her to as a child had had those concerns as well. Euphemia Potter had done her very best to teach Catherine all she could until the fateful day when Professor Dumbledore showed up on their doorstep and assured them that she would be able to learn perfectly well at Hogwarts. And it was clear now how right he was, having excelled at the school and left with five NEWTs.

"My mother took Narcissa away somewhere to spare Father killing her. She was only a few months old, and we were never allowed to talk about her again." Bellatrix held the photo up again. "This is the only surviving evidence that she existed at all. I hid it from my parents. Not even my sister remembers."

'I'm not her,' Catherine wrote, glaring at the woman. She was not from a dark family like the Blacks, she was sure of it. She knew all about their kind. Her little brother was best friends with Bellatrix's cousin and he often spoke of the horrible things that went on inside their ancestral homes. She wanted nothing to do with them.

"You have no proof that you're not," Bellatrix countered.

Catherine suddenly found herself alone as the older woman simply walked away. And just like that, Catherine's reality came crumbling down around her.

It was still early in the fall which meant James was away at school, so dinner at the Potter house was relatively quiet. Catherine came home to feast prepared by her mother and, while she was grateful for the food, she couldn't bring herself to smile and hug her parents as she usually did.

'Something happened at work today,' she signed to them. Her notepad was only used for communicating with strangers. Any close friends or family took the time to learn Muggle sign language. 'Do you know Bellatrix Black?'

Her parents shook their heads. "Is that one of Sirius' cousins?" her dad guessed from the name. "Cygnus showed me a picture of the girls years ago, when they were quite young. I haven't seen them since."

'She spoke to me today. She claims she once had a second sister.'

Euphemia's shoulders fell and Catherine felt bad for bringing this subject up. She knew well how hard her parents had tried for a child before they'd been blessed with her and James. There had been so many miscarriages, and it was still hard for them to talk about.

"It happens sometimes, dear."

"Especially in those families," her father continued. "Inbreeding leads to severe complications sometimes. If Cygnus had another child … it's not surprising. And if she died, they wouldn't have mentioned it."

'Bellatrix seems to think that I'm her missing sister.' Catherine watched her parents' reactions carefully, gauging for any sign that it was true. 'She says that her sister was deaf and that Cygnus wanted to kill her, but her mum hid her somewhere when she was a baby.'

Her parents shared a look and Euphemia looked close to tears when she looked back at Catherine.

'Am I adopted?'

"You're ours," Fleamont claimed, though there was a slight droop to his shoulders that was never there before. "We raised you, and that's all that matters."

"But we don't know whose you were originally." Euphemia was crying now. "I found you in the alley behind Eeylop's. You were so little, and helpless. There was no one else in sight. We took you to the hospital and they told us about your condition and …"

"We knew," Fleamont signed. "The moment we heard about your condition, we knew you had to be from one of those bloody families and they just threw you away because you were different."

"We couldn't have children, no matter how hard we tried. It was a miracle, finding you. The hospital let us adopt you right away."

Catherine found herself sobbing, quickly wiping her tears away to be able to see her parents' hand gestures. She was furious, but not at them. They had been saints to look after her. But the Blacks, it seemed, were just as cruel as Sirius had let on.

'It's okay,' she signed to them, forcing herself to calm down for their sakes. 'I'm not upset, I promise. You're my parents and you always will be and … and nothing they did matters.'

Euphemia rushed forward to hug her daughter and Catherine melted into the embrace, but she was still angry.

Catherine didn't see Bellatrix again for two weeks. They were in different departments of the Ministry and, Catherine suspected, on different sides of the growing war.

She had resigned herself to being unsatisfied for the rest of her life. She would never get closure over being thrown away like trash, and her anger flared every time she thought about it. And then she found herself alone in the Ministry lift with Bellatrix.

"Have you looked into what I told you about?" Bellatrix asked, smirking.

Catherine couldn't meet her gaze. She scribbled a quick note. 'I want to see your parents.'

She could see Bellatrix laughing and it made her angrier.

"They won't be happy about this, but alright. I think it's time we had a family reunion."


End file.
